VBA assigns incorrect value to variable - vba

Question

I have a function in VBA, which is a part of a bigger setup. The function resides inside a Class Module, and is basically just a glorified subtraction. I wondered why I got some weird results, so I (over-)simplified the function for debugging purposes. It turns out, that one of the variables isn't assigned the value that it should, but rather some seemingly random value. How can a simple assign go so wrong?
And even weirder, why does it not always it assigns the incorrect value? It only happens sometimes. Other times it is correct. And occationally it seems like nothing is evaluated at all, and the function just returns 0 (zero).
From all I can see it cannot be an issue with my code, but rahter with the way VBA works (behind the scenes). But as long as I do not understand it, it is quite difficult to mitigate.
Code:
Public Property Get MySubtractionFunction() As Double
Dim tmpValue1 As Double
Dim tmpValue2 As Double
Dim tmpOutput As Double
'When debugging, sometimes CDbl(Me.Value2) evaluates to approximately 18.000
'However tmpValue2 evaluates to approximately 10.000
tmpValue1 = CDbl(Me.Value1)
tmpValue2 = CDbl(Me.Value2)
tmpOutput = tmpValue1 - tmpValue2 'Breakpoint is set at this line
tmpOutput = Application.WorksheetFunction.Min(tmpOutput , tmpValue1)
'Return output
MySubtractionFunction= tmpOutput
End Property
Update 1
When I hover the mouse over Me.Value2 before reaching the breakpoint, it actually shows the value that is assigned to tmpValue2. If I then remove the mouse, and hover back over Me.Value2 again, then it shows a different value. How can a property value just change like that, without any code being executed?
Update 2
Maybe I should mention that the problem only arises when I use the Class Object inside a loop. It is called like this:
For i = 1 To 1000
Dim myObject As myClass
Set myObject = New myClass
'Some initialization
result = myObject.MySubtractionFunction
'A bunch of other stuff
Set myObject = Nothing
Next i

Answer 1

All computer languages have a huge problem, when they are dealing with doubles (floating points). Thus, in C#, you should use decimal to avoid this problem. In Excel, you should round.
Take a look at what Microsoft says about it:
https://support.microsoft.com/en-us/help/78113/floating-point-arithmetic-may-give-inaccurate-results-in-excel

Answer 2

Solution
As I mentioned, the property I had an issue with, was the last in a chain of many. All calling other properties of the class module (except the first in the chain). The problem originated quite early, and chained through all the steps.
The reason it was so difficult to identify, was that the property value which was initially incorrect, was updated when I hovered the mouse over the variable to inspect the variable, in debugging mode.
The solution was to expand all the steps in the chain, in a manner similar to that in the original post. This is not always required, since the problem only showed when I ran a multiple of calculations rapidly. But if anyone expeirence similar problems, I would suggest you try this fix.
This did not work:
Public Property Get myProperty() As Double
myProperty = Me.someOtherProperty + Me.aThirdProperty
End Property
This did:
Public Property Get myProperty() As Double
Dim tempSomeOtherProperty As Double
Dim tempAThirdProperty As Double
Dim tempResult As Double
tempSomeOtherProperty = Me.someOtherProperty
tempAThirdProperty = Me.aThirdProperty
tempResult = tempSomeOtherProperty + tempAThirdProperty
myProperty = tempResult
End Property